The present invention relates to a structure of a printer head for a dot-printer, in particular, relates to such a printer head which is small in size, having excellent printing quality, can be manufactured through a simple process, and can operate with less power consumption.
FIG. 1 shows the principle of the dot matrix printing in a serial printer. A printer head 100 has eight needles for mosaic printing, and travels along a printing line in the direction of the arrow A. During the travelling, needles are selectively driven to hit a paper through an ink ribbon and a desired pattern "A", "B", "C" or "D" is printed. The selection of needles is controlled by the content of an integrated circuit (IC) memory. When the size of a character to be printed is 2.67 mm.times.2.05 mm, 7.times.5 number of dots are enough for printing a recognizable character.
The prior needle dot head for dot printing process is shown in the U.S. Pat. No. 3,896,918, in which an electromagnetic drive for the operation of printing needles of a mosaic printing head includes a pivotally mounted armature for each needle which are arranged along circular arc. The construction includes a common yoke for all of the electromagnets which comprises two concentric cups or walls forming a single unit with cylindrical cores arranged at equal intervals along a circular arc parallel to the genatrix of the cup and located between the individual yoke cups.
However, said prior printing head has the disadvantages that the power consumption for driving needles is large, the size of the apparatus is large, and the operational speed of the printer is rather slow. Those disadvantages come mainly from the fact that a needle is driven by an electromagnet, and all the printing power for striking a paper by a needle is given by said electromagnet.
The present inventors have proposed a printing head for a dot printer for overcoming said disadvantages in Japanese Patent Application No. 56924/79, 56925/79 and 62143/79 (corresponding U.S. application Ser. No. 147,106, U.K. Application No. 8,014,271, West Germany Application No. P 30 17 903.4). That printer head comprises of a cylindrical permanent magnet, a first yoke covering the bottom of the permanent magnet, a plurality of electromagnets each positioned on a circle on said first yoke with the predetermined angle intervals, a disk shaped spring having an outer ring and a plurality of projections towards the center of the disk, a plurality of armatures each attached to the related projection of said disk spring, a plurality of print needles each attached to the related projection of said disk spring so that each of the needles has the perpendicular component to the disk spring plane, a ring shaped spacer positioned between the disk spring and said cylindrical permanent magnet, a second yoke for providing a magnetic flux path between the permanent magnet and each of the electromagnets, and a guideframe having a thin linear slit for arranging the top of said needles and covering the needles.
The present invention is the improvement of that proposed printing head, and has the advantages that the manufacturing process is simple, the manufacturing cost is low, and the operational life time is long.